Pollinator dependence and pollination deficit in Hedera helix, and effects on frugivore feeding choices

Abstract

English ivy (Hedera helix) is an important resource for wildlife in rural and urban ecosystems. It provides pollen and nectar for flower-visiting insects during autumn and fruits for frugivores during winter and spring. A requirement of insect pollination for fruit set in ivy implies that recent declines in pollinator populations can threaten food supply for frugivores. This study investigated the link between pollination services and the quantity and quality of fruit produced in ivy, and how that could in turn influence frugivore feeding choices, in a mixed woodland and an urban garden habitat respectively. Surveys on pollinator community and activity were conducted to assess the overall level of pollination. A set of experiments involving insect exclusion, open pollination, and extra pollen supplementation was performed to reveal the level of pollinator dependence and pollination deficit in ivy. Additionally, the removal of these fruits by frugivores was measured to test whether frugivore feeding preferences are influenced by the initial level of pollination. Our results showed that the quantity and quality (size) of fruit produced in ivy were significantly reduced under insect exclusion, which is strong evidence for pollinator dependence. Pollination deficit was also identified at both sites. Furthermore, the data indicate that frugivores can display some degree of preference for well-pollinated ivy fruits. Taken together, our study shows that declines in pollination services will have direct impacts on the availability and quality of ivy fruits for frugivores. Maintaining the health of pollinator communities in both urban and rural habitats could therefore ensure healthy ecosystem functioning.